1. Field of the Invention
The invention relates to optical blood hemostatic analysis apparatus and methods, and more particularly to an apparatus and method for optically measuring the functional capacity of blood platelets and the blood clotting system.
2. Related Art
In the medical field, it is often desirable to measure and evaluate blood clotting times and blood platelet function. For example, studies of platelet function and coagulation time are useful in the identification of patients who are at increased risk of thrombosis due to platelet hyperactivity or to blood hypercoagulability. They are also of use in the identification of patients who are at risk of bleeding due to platelet hypoactivity or to blood hypocoagulability. Devices for measuring these aspects of blood are therefore quite useful.
Separate blood clotting evaluation instruments and platelet function evaluation instruments have been known in the art. A number of machines on the market for evaluation of blood clotting utilize a light beam for detecting the clotting end-point, but can only be used with plasma (a relatively clear fluid derived by removing the red cells). Very few blood clotting evaluation instruments can be used with both opaque whole blood and with plasma, but these are all believed to require physical contact with the specimen, and thus contain parts that are an infection hazard and must be carefully cleaned to avoid infectious propagation. In addition, such devices are difficult to clean reproducibly, potentially affecting test performance. This latter class of machine often uses a primarily mechanical end-point detector, and, for that reason, is prone to breakdown. One example of such an instrument is known as a fibrometer, which uses a metal probe.
Devices also exist capable of evaluating platelet function. It is believed that all of these machines operate with plasma and are single purpose instruments. These machines are generally called platelet aggregometers. Aggregometers generally transmit a light through a suspension of platelet rich plasma (plasma containing platelets) incubated at 37.degree. C. (body temperature). Light shining through the suspension is generally refracted by the moving platelet surfaces. When aggregating substances are added, the platelets clump into large aggregates. This causes more light to get through to a photosensor on the far side of the measuring chamber, generating a detectable signal.
There is one aggregometer instrument available that purports to perform platelet function studies on whole blood (Chronolog Corporation, Haverstown, Pa.). It is believed that this device does not measure the formation of platelet aggregates, but rather the adherence of already formed platelet aggregates to a pair of metal wires. In addition, it cannot perform any clotting studies.
One reference is known that describes a device for optical indication of coagulation and concentration and aggregation of platelets, but can only be used with plasma (see U.S. Pat. No. 4,501,491). This reference also cites a number of other references in the field (see column 2).
It is therefore desirable to provide a single instrument that can analyze blood platelet function and clotting evaluation using whole blood. It is also desirable that such a machine not require physical contact between the whole blood specimen and the analysis elements.